1. Field of Invention
The present invention relates to the design of an alternating current (AC) light-emitting diode (LED) device and its manufacturing process based on GaN epitaxial growth on transparent sapphire substrate. This design incorporates a special layout of LED cells monolithically integrated to form an LED device which can be directly connected to AC power sources 120V, 220V or other voltages without AC to DC drivers.
2. Description of the Related Art
LEDs are semiconductor diode devices to produce light when the diodes are forward biased and the recombination of electron and hole pairs release energy in the form of photons. Traditional light sources, such as incandescent lamps, which rely on visible portion of the thermal radiation from the filament heated to very high temperatures, and compact fluorescent lamps, which use discharge from mercury vapor and argon gas to generate UV light to excite luminophore for visible light. LED, a solid lighting device, has numerous advantages over traditional lighting options, including compact size, long lifetime, high durability, low power consumption, and absence of harmful mercury. LEDs are widely used as indicator lights, vehicle signal and illuminating lights, LCD backlights for TV and mobile devices, projector light sources, outdoor display and general illumination or lighting.
LEDs are low voltage DC devices that let electron pass in one direction and block electron flow when connected in the opposite polarity. They are driven by either DC voltage sources or by AC voltages with AC to DC drivers to supply the desired DC voltage.
To allow LEDs to directly connect to the AC power sources without using AC to DC drivers, two sets of LEDs are connected in parallel with opposite polarity, as described by Okuno et al in U.S. Pat. No. 4,298,869 entitled “LIGHT-EMITTING DIODE DISPLAY” and Reymond in U.S. Pat. No. 5,936,599 entitled “AC POWERED LIGHT EMITTING DIODE ARRAY CIRCUITS FOR USE IN TRAFFIC SIGNAL DISPLAYS”. Their approaches were based on expensive discrete single LED emitters and also required complex wiring and assembly process. Fan et al in U.S. Pat. No. 6,957,899 B2 entitled “LIGHT EMITTING DIODES FOR HIGH AC VOLTAGE OPERATION AND GENERAL LIGHTING” proposed the design of a single high voltage LED chip, composed of two arrays of series-connected individual LEDs in opposite polarity for connection to high voltage AC sources. The design doubles the number of LED diodes in the chip to achieve the same amount of light output from similar DC driven LED device. Hall et al in U.S. Pat. No. 2004/0075399 A1 entitled “LED LIGHT ENGINE FOR AC OPERATION AND METHODS OF FABRICATING SAME” proposed a chip layout design to deal with issues related to individual open or short diode in the series-connected chains. Lee et al in the U.S. Pat. No. 7,834,364 B2 entitled “AC LIGHT EMITTING DIODE AND METHODE FOR FABRICATING THE SAME” adopted a similar approach as described by Fan et al, and described how the individual LEDs were connected to form a single AC LED chip. Lin et al in the U.S. Pat. No. 7,474,681 B2 entitled “ALTERNATING CURRENT LIGHT-EMITTING DEVICE” proposed a different design to incorporate multiple active layers with a rectifier bridge in the design so the active layers take turns to emit light with different colors when powered by AC voltage sources. There are no specifics regarding how to incorporate the rectifier bridge and how to handle specific AC line voltages. Lee et al in another U.S. Pat. No. 7,964,880 B2 entitled “LIGHT EMITTING ELEMENT WITH A PLURALITY OF CELLS BONDED, METHOD OF MANUFACTURING THE SAME, AND LIGHT EMITTING DEVICE USING THE SAME” described a lateral and a vertical chip with LED cells monolithically connected to take high DC voltage and also connected to an external predetermined rectifier bridge to handle AC voltage. However, there were no specifics regarding how to integrate the rectifier bridge into the LED chip design, and how to handle different AC line voltages.
Therefore, a need exists to develop a novel alternating current light-emitting diode chip, based on flip-chip technology, to address the drawbacks of the previous art, and to provide a lower cost and a more reliable solution for the general lighting industry.